Tap grinding fixture



y 4 L. F. souTHwlcK Ei-AL I 2,420,572

TAP GRINDING FIXTURE Filed Jan. 10, 1946 3 Sheets-Sheet l FINVENTORS[4035x105- Saar/mack BY Ross/7Z7? A? Hou- ATTOEZVEY 35 M q EEFEPQ May13, 1947. souf w c ETAL 2,420,572

I'AP GRINDING FIXTURE Filed Jan. 10, 1946 3 Sheets-Sheet 2 ATTORNEY y13, 1947- I F. SOUTHWICK ETAL 2,420,572

TAP GRINDING FIXTURE Filed Jan. 10, 1946 3 Sheets-Sheet 5 II II I ENTORI[AUfiE/VG'f/FSOUTHMCK f fiassxrew/Rflur Z41 26 f2 ATTORNEY Patented May13, 1947 TAP GRINDING FIXTURE Laurence F. Southwick, Mcriden, andRossiter R. Holt, Manchester, Conn.

Application January 10, 1946, Serial No. 640,273

11 Claims. 1

This invention relates to abrading apparatus and more particularly to atap-grinding fixture for grinding the forward end of a tap to anydesired angle of chamfer and degree of relief.

One object of the present invention is to provide a tap-grinding fixtureof the above nature having means to hold the tap in any desiredeccentric position so as to permit the production of the desired chamferby a grinding wheel engaging the tap.

A further object is to provide an attachment of the above nature havingan inwardly-extending locating stud which is adapted to engage in theflute between any two adjacent lands of the tap for holding the tapstationary during the grinding of the point of a land thereof.

A further object is to provide an attachment of the above nature whichmay be used upon a lathe, surface grinder, tool grinder, hand grinder,or any other machine adapted to support a tap between centers, whereinone center is provided by the attachment and the other center isprovided by said machine.

A further object is to provide an attachment of the above nature whichis supplied with a longitud-inal shank for replacing'one center of themachine being used.

A further object is to provide a device of the above nature which willbe simple in construction, inexpensive to manufacture, easy to installand manipulate, compact, precise, ornamental in appearance, having theminimum of backlash, and very eflicient and durable in use.

With these and other objects in view, there have been illustrated on theaccompanying drawings two forms in which the invention may convenientlybe embodied in practice.

In the drawings,

Fig. 1 represents a top plan view of a tap grindatta'chment embodyingthe invention.

Fig; 2 is a longitudinal sectional view of the same, taken along theline 22 of Fig. 1, looking inthe direction of the arrows.

Fig. 3 is a transverse sectional view, taken along the line- 3-3 of Fig.1.

Fig. 4 is a detail sectional view showing the locating stud in operatingposition within one of the flutes of the tap, said section being takenon the-line 4-4- of Fig. 1.

Fig. 5 is a sectional View, taken along the line- '.i5 of Fig. 1 lookingin a direction opposite from the view shownin Fig. 3.

Fig; 6- is a side view on a smaller scale of a modified form of theinvention employing an angular carrier arm for holding the locatingstud.

Fig. 7 is a rear view of the same, similar to the view shown in Fig. 5.

Fig. 8 is a front view of the same, similar to the view shown in Fig. 3.

Fig. 9 is a front elevation of the same.

Fig. 10 is a longitudinal sectional view of the same, taken through thebarrel of the attachment.

In the first form of the present invention, the tap to be ground, whichmay have any number of flutes, will be accurately located by a radialstud which engages in a flute of the tap. The locatin stud is adjustablymounted within a side carrier arm which may be located at any one ofseveral angular positions with respect to the barrel of the attachment,and will be held in operating position by a cap screw which is engagedin any one of a series of tapped holes in said barrel.

In the second form of the invention, the angular carrier arm is securedto the barrel by a single clamp screw, permitting the locating stud toengage in a flute of the tap adjacent the land being ground, or remotetherefrom.

An important feature of both forms of the invention is the use of arectangular pivotal center plate which supports the point of the tap atits center, and which may be shifted eccentrically about its pivot withrespect to the center of rotation of the barrel of the attachment. Thecenter plate is pivoted at one end on the barrel, and provided near itsother end with an arcuate slot into which fits a cap screw for lockingsaid plate at any desired eccentricity. When this center plate isshifted in one direction, right hand taps may be ground, and it will beoppositely shifted for left hand taps.

First form Referring now to the drawings in which like referencenumerals denote corresponding parts throughout the several views, thenumeral ID indicates a hollow cup-shaped barrel or head having arectangular center plate [I pivotally mounted on a shoulder screw I I0located in the forward closed end of said barrel. The center plate I!)is adapted to be held in adjusted position by a Washer Ilb engaged bythe head of a clamping screw I la which is fitted loosely within anarcuate slot Ild.

The numeral ['2 indicates a longitudinal conical center which is carriedby the plate 5-9, and the numeral l3 indicates a rearwardly-extendingjournal which has a tapered recess l-Ba toreceive a taper arbor (notshown).

Mounted upon the journal 13' isa split clamping collar [4 which isprovided with a radial slot I la through which extends a headed lockingscrew [5 which is screwed into one side thereof for securely clampingthe collar [4 upon the journal l3.

In order to locate the tap T in accurate position with respect to agrinding wheel 30, to be later described, provision is made of alongitudinal carrier arm I-B having a slotted section lBa for receivinga headed clamp screw 21, to be described later.

The free end of the carrier arm I6 is provided with a tapped hole forreceiving a split bushing l9 which surrounds and clamps upon a radiallocating pin or stud I! provided with a reduced rounded cylindrical tipIla which is adapted to engage in a flute 32 of the tap T, at a pointsubstantially opposite the land 33 being ground. The locating pin I1 isprovided with a knurled clamping nut I8 which is fitted upon the bushingI9, the latter being provided with reversely tapered threads on its endsfor fitting within the carrier arm [6 and the nut 18, respectively.

In order to limit the rotation of the barrel EB, provision is made of aradial stop pin 26 on the collar I4 and a longitudinal stop pin 2|secured rigidly to the rear end of said barrelsaid pins 20 and 2| beingin alignment with each other.

The journal l3 is adapted to be fitted within an oilite bearing 22,which is tightly fitted over the end of said journal. The assembly ismaintained in place by a retaining ring 23 fitting within a groove 28formed in the barrel Ill.

Provision is also made of a steel washer 25 which presses a felt washer25 against a shoulder 26a of the oilite bearing 22.

The other center of the machine is indicated by the numeral 28, and isprovided with a fixed conical section 29 adapted to engage the rearportion 29a of the tap T.

The grinding wheel 30 is mounted upon a motor-driven spindle 1 3i and isadapted to be swun against the end of the land of the tap T for grindingit accurately to any desired angle of chamfer.

In order to permit the carrier arm l3 to be selectively secured in anyone of four positions around the axis of the barrel l8, depending on theposition of the land to be engaged by the locating stud, provision ismade in the circumference of said barrel of four radial tapped holes 34,35, 3B, 3! adapted selectively to receive the clamp screw 21 therein.

Operation of first form In operation, the conical center l2 of theattachment will first be adjusted to the desired degree of relief byswinging the center plat H about the shoulder screw lie on which it ispivoted. The point P of the tap T will then be placed on the center [2and the rear of the tap 25% will be engaged by the other conical center29 of the lathe or other machine, as shown in Fig. l.

The locating pin I! will then he slid inwardly with respect to thecarrier arm 16 until the locating tip I la thereof engages at thedesired point of the flute 32 of the tap T.

The grinding wheel 3d will then be adjusted to any desired chamferangle, after which it will be brought into cutting position bymanipulating the cross feed (not shown) of the machine.

It will be understood that if desired, the an gle of chamfer may also bevaried by shifting the axis of the grinding wheel 3!] or the center 29of the machine. The periphery of the grinding wheel 30 may also bedressed to any desired angle.

The locating stud I! may then be used as a handle to rotate the barrelI0 and the carrier arm L6 as a unit until the land to be ground isbrought into contact with the grinding wheel and is ground thereby tothe desired extent. After the grinding of each land is completed, thelocating stud II will be withdrawn and inserted within the next flute 32of the tap T. This operation will be repeated until all the lands 33 ofthe tap have been ground.

One advantage of the present invention is that by limiting the movementof the barrel H] by the stop pins 20, 2|, the operator is prevented fromswinging the fixture so far that it will damage the next adjacent land.

Modified form In the modified form of the invention, shown in Figs.6-10, provision ismade of a dowel pin 50 for pivotally securing thecenter plate I I to the barrel ID. This form of the invention is alsoprovided with a set of thrust ball bearings 52 to reduce the frictionduring the operation of the attachment.

More-over, instead of providing a straight carrier arm l6 for thelocating stud I l, as in the first form of the invention, an angularcarrier arm 53 having a slot 54 in its longitudinal section is employed.The arm 53 is adapted to be secured to the barrel I 0 by means of theclamp screw 27 which fits within a single tapped hole 55 in the barrelIll.

The angular shape of the carrier arm 53 permits taps having two flutesas well as those having three or more flutes to be accurately locatedduring the grinding of the points thereof.

The present invention is especially adapted for use in small machineshops, and is capable of performing efficient work with more accurateresults than previous tap grinding attachments now on the market.

While there have been disclosed in this specification two forms in whichthis invention may be embodied, it is to be understood that these formsare shown for the purpose of illustration only, and that the inventionis not to be limited to the specific disclosures, but may be modifiedand embodied in various other forms without departing from its spirit.In short, the invention includes all the modifications and embodimentscoming within the scope of the following claims.

Having thus fully described the invention, what is claimed as new, andfor which it is desired to secure Letters Patent, is:

1. In a tap-grinding fixture, a barrel, a support therefor, a centerplate pivotally secured to the inner face of said barrel, said platehaving a tapered center, means to swing said plate about its pivotalaxis to vary the eccentricity of said center, a carrier arm rigidlysecured to the circumference of said barrel and rotatable with saidbarrel as a unit, and a radial locating stud secured to said carrier armand adapted to engage a flute of the tap being ground by a grindingwheel, said stud serving as a handle to rotate the tap eccentricallyabout the axis of the barrel so that the desired degree of relief may beobtained during the grinding of each tap land.

2. The invention as defined in claim 1, in which said center plate hasan arcuate slot spaced from the pivot thereof, a stud mounted on the endof said barrel located in said slot, and a clamping screw for holdingsaid plate in rigid position with respect to said stud.

3. Th invention as defined in claim 1, in which said carrier arm ismounted on an axis parallel to the axis of said barrel, and is slottedto permit adjustment relative to said barrel in a longitudinaldirection.

4. The invention as defined in claim 1, in which said barrel is providedon its circumference with a plurality of tapped holes for selectivelyreceiving a clamping screw for holding said carrier arm in adjustedposition.

5. The invention as defined in claim 1, in which said barrel is mountedto rotate upon a bearing surrounding a journal which is secured to saidsupport.

6. The invention as defined in claim 1, in which an anti-frictionbearing is provided between said support and said barrel to reduce thefriction thereof.

7. The invention as defined in claim 1, in which said carrier arm isangle-shaped so as to permit said locating stud to engage a tap fluteadjacent to or remotefrom the land being ground.

8. In a tap-grinding fixture, a barrel, a support therefor, a centerplate pivotally secured to the inner face of said barrel, said platehaving a tapered center, means to swing said plate about its pivotalaxis to vary the eccentricity of said center, a carrier arm rigidlysecured to the circumference of said barrel and rotatable with saidbarrel as a unit, and a radial locating stud secured to said carrier armand adapted to engage a flute of the tap being ground by a grindingwheel, said stud serving as a handle to rotate the tap eccentricallyabout the axis of the barrel so that the desired degree of curved reliefmay be obtained during the grinding of each tap land.

9. The invention as defined in claim 1, in which said locating stud isslidably mounted in said carrier arm whereby it may be quicklydisengaged from the flute of said' tap.

10. In a tap grinding fixture, a hollow rocking barrel, said barrelcarrying a radial locating stud for engaging a flute of the tap to beground by a grinding wheel, a journal located within said barrel, asplit collar clamped upon said journal, and coacting stop means on saidbarrel and said collar to limit th rotation of said barrel during theoperation of grinding the point of said tap.

11. The invention as defined in claim 1, in which said tap locating studhas a bushing mounted thereon, the ends of said bushing being reverselythreaded, the end of said carrier arm being screwed on one end of saidbushing, the other end of said bushing being split and tapered andhaving a lock nut mounted thereon.

LAURENCE F. SOUTHWICK. ROSSITER R. HOLT.

